Tax Matters - Reconciliation of Gross Unrecognized Tax Benefits - Footnotes (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|---|---|
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | $ 5,381 | $ 6,259 | $ 6,558 | $ 5,826 |
| Income Taxes Payable [Member] | ||||
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | 108 | 11 | ||
| Current Tax Assets [Member] | ||||
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | 2 | 1 | ||
| Noncurrent Deferred Tax Assets And Other Noncurrent Tax Assets [Member] | ||||
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | 51 | 47 | ||
| Noncurrent Deferred Tax Liabilities [Member] | ||||
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | 2,800 | 3,200 | ||
| Other Taxes Payable [Member] | ||||
| Income Tax Contingency [Line Items] | ||||
| Unrecognized tax benefits | $ 2,400 | $ 3,000 |